The present invention relates in general to platter systems which are used in conjunction with projectors in movie theaters for showing movies, and in particular, to a new and useful safety apparatus for avoiding a condition known as head wrap, where the film is inadvertently wrapped a multiplicity of times around a stationary central area of the platter system when the platter rotates too quickly, to slowly or fails to rotate at all.
Full length movies are currently supplied to movie houses on multiple reels which each carry only enough film for approximately 1/2 hour of showing. In the past a projectionist was required to operate multiple projectors which were mounted with one of the reels to avoid interruption in the movie as the projection function would shift from one projector to another.
More recently, movie houses have adopted the use of a platter system which comprises two or more platters which may each encompass the entire full length feature. The multiple reels are spliced together and then stored in a horizontally extending spool on one of the platters in the platter system. The film is fed from that platter to a projector and then back to a take up platter of the platter system. For the next showing, the take up platter is used as the feed platter with the film being rethreaded through the projector for showing the film in the proper direction.
The projector which functions to bring each frame of the film into the proper position for projecting its image onto a screen, operates at a constant speed.
The platter system which feeds the film to the projector and takes up the film from the projector is controlled independently from the projector and has a variable speed.
The platter operating as the take up platter and under normal conditions rotates at a speed sufficient to take up the film being fed from the projector. The take up platter is operated by a take up speed control which maintains constant tension on a film as it moves along a take up path from the projector. A fail safe switch is known for mounting under the projector. the fail safe switch has a roller which rolls against the taught film moving along the take up path. The roller is connected to a pivotable arm which engages the fail safe switch. When film tension is lost, the arm pivots to activate the switch. Film tension is lost due to a break in the film or at the end of a film. The fail safe switch is connected in such a way to cut power to the projector.
The other platter in the platter system which feeds the film is referred to as the feed out platter. Under normal conditions the feed out platter will supply film at a rate at which it is needed by the projector. The demand is constant but the speed of rotation of the feed out platter is not. The speed of the feed out platter increases and decreases in cycles throughout the entire length of the movie. This is due to the design of the feed out control mechanism and results in very little film tension on the film of the feed out film path to the projector.
Head wrap is a condition which occurs on the feed out platter due to a mismatch in supply and demand between the feed out platter and the projector. It is caused by the feed out platter rotating too fast or too slow or not at all for an extending period of time. Under normal conditions there is no film tension on the feed out path. Under a head wrap condition there will be film tension which increases proportionally to the amount of film that has been wrapped around the fixed central area or head of the platter. Once the head wrap condition has begun it will continue without interruption until a threshold of tension is reached when the film will either break, damage rollers and film guides, sprockets, become jammed in the projector and melt or some combination of the foregoing. A head wrap can be the result of many possible problems including operator error, faulty equipment or damaged film. Normally a head wrap condition is not realized until the movie has been interrupted. It often requires more than an hour's time to correct the damage. This usually results in refunds to the movie patrons and general confusion in the movie theater. Although a safety mechanism in the form of the fail safe in the take up path is known, there is no known safety mechanism for the film in the feed path. This may be due to the more passive role of the feed out platter and its feed out path, which, upon breakage or the end of a film, is perceived to suffer no ill effects.
A need thus remains for a mechanism to avoid head wrap conditions in currently used and available film platter systems.